MongoDB查询时被锁住的问题
1. 背景
mongoDB版本1.8.1
collection stats
| > db.user.gift.stats() { "ns" : "statgame.user.gift", "count" : 650, "size" : 162804, "avgObjSize" : 250.46769230769232, "storageSize" : 696320, "numExtents" : 4, "nindexes" : 3, "lastExtentSize" : 524288, "paddingFactor" : 1.0099999999999576, "flags" : 1, "totalIndexSize" : 180224, "indexSizes" : { "_id_" : 40960, "day_1_userId_1_fromId_1_sceneId_1" : 81920, "idx_modified_time_long" : 57344 }, "ok" : 1 } |
indexes
| > db.user.gift.getIndexes() [ { "name" : "_id_", "ns" : "statgame.user.gift", "key" : { "_id" : 1 } }, { "name" : "day_1_userId_1_fromId_1_sceneId_1", "ns" : "statgame.user.gift", "unique" : true, "key" : { "day" : 1, "userId" : 1, "fromId" : 1, "sceneId" : 1 } }, { "name" : "idx_modified_time_long", "ns" : "statgame.user.gift", "key" : { "modifiedTimeLong" : -1 } } ] |
stored data的结构
| > db.user.gift.find().limit(1) { "_id" : ObjectId("4dad7840c8b4ebc1064a1f25"), "day" : ISODate("2011-04-18T16:00:00Z"), "earnMoney" : NumberLong(18), "earnTimes" : NumberLong(1), "fromId" : NumberLong(17441), "modifiedTimeLong" : NumberLong("1303214144458"), "receiveMoney" : NumberLong(30), "receiveTimes" : NumberLong(1), "sceneId" : NumberLong("216172782113787850"), "userId" : NumberLong(4037) } |
2．在shell查询时不小心将sceneId的值直接输入了，mongoDB认为shell输入的都是double类型，而sceneId是长整型。216172782113787850为58bit。
| db.user.gift.find({$query:{day:{$gte:new Date(2011,03,05),$lte:new Date()}, sceneId:216172782113787850}, $orderby:{day:-1}}) |
这时这个查询会被block住。查看currentOp的执行情况。
| > db.currentOp() { "inprog" : [ { "opid" : 756, "active" : true, "lockType" : "read", "waitingForLock" : false, "secs_running" : 597, "op" : "query", "ns" : "statgame.user.gift", "query" : { "$query" : { "day" : { "$gte" : ISODate("2011-04-04T16:00:00Z"), "$lte" : ISODate("2011-04-25T03:22:09.948Z") }, "sceneId" : 216172782113787840 }, "$orderby" : { "day" : -1 } }, "client" : "127.0.0.1:58166", "desc" : "conn" } ] } |
用top看系统资源使用情况：
| top - 11:34:04 up 2:57, 6 users, load average: 1.67, 1.13, 0.64 Tasks: 145 total, 3 running, 141 sleeping, 1 stopped, 0 zombie Cpu(s): 50.2%us, 0.2%sy, 0.0%ni, 49.6%id, 0.0%wa, 0.0%hi, 0.0%si, 0.0%st Mem: 4048136k total, 2092240k used, 1955896k free, 213088k buffers Swap: 3068404k total, 0k used, 3068404k free, 936064k cached
PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND 3527 root 15 0 333m 21m 20m R 99.6 0.5 12:58.16 mongod 7050 root 19 0 1604m 655m 8512 S 2.3 16.6 2:53.05 java |
占CPU接近100%，泪奔。
使用new NumberLong(“sceneId”)来查询，没有问题
| > db.user.gift.find({$query:{day:{$gte:new Date(2011,03,05),$lte:new Date()}, sceneId:new NumberLong("216172782113787850")},$orderby:{day:-1}}) { "_id" : ObjectId("4db00226c8b4ebc1064a8b76"), "day" : ISODate("2011-04-19T16:00:00Z"), "earnMoney" : NumberLong(0), "earnTimes" : NumberLong(0), "fromId" : NumberLong(4124), "modifiedTimeLong" : NumberLong("1303380518261"), "receiveMoney" : NumberLong(50), "receiveTimes" : NumberLong(1), "sceneId" : NumberLong("216172782113787850"), "userId" : NumberLong(4124) } { "_id" : ObjectId("4db00226c8b4ebc1064a8b75"), "day" : ISODate("2011-04-19T16:00:00Z"), "earnMoney" : NumberLong(1005), "earnTimes" : NumberLong(113), "fromId" : NumberLong(4042), "modifiedTimeLong" : NumberLong("1303380518320"), "receiveMoney" : NumberLong(3350), "receiveTimes" : NumberLong(113), "sceneId" : NumberLong("216172782113787850"), "userId" : NumberLong(4124) } ……………….. |
将userId的值直接输入查询，userId目前小于4字节。没有问题。4字节整数是可以输入直接查询的。
| > db.user.gift.find({$query:{day:{$gte:new Date(2011,03,05),$lte:new Date()}, userId:4124},$orderby:{day:-1}}) { "_id" : ObjectId("4db0021cc8b4ebc1064a86f3"), "day" : ISODate("2011-04-20T16:00:00Z"), "earnMoney" : NumberLong(1503), "earnTimes" : NumberLong(167), "fromId" : NumberLong(4042), "modifiedTimeLong" : NumberLong("1303380509069"), "receiveMoney" : NumberLong(5010), "receiveTimes" : NumberLong(167), "sceneId" : NumberLong("792633972503933553"), "userId" : NumberLong(4124) } { "_id" : ObjectId("4db00226c8b4ebc1064a8b76"), "day" : ISODate("2011-04-19T16:00:00Z"), "earnMoney" : NumberLong(0), "earnTimes" : NumberLong(0), "fromId" : NumberLong(4124), "modifiedTimeLong" : NumberLong("1303380518261"), "receiveMoney" : NumberLong(50), "receiveTimes" : NumberLong(1), "sceneId" : NumberLong("216172782113787850"), "userId" : NumberLong(4124) } { "_id" : ObjectId("4db00226c8b4ebc1064a8b75"), "day" : ISODate("2011-04-19T16:00:00Z"), "earnMoney" : NumberLong(1005), "earnTimes" : NumberLong(113), "fromId" : NumberLong(4042), "modifiedTimeLong" : NumberLong("1303380518320"), "receiveMoney" : NumberLong(3350), "receiveTimes" : NumberLong(113), "sceneId" : NumberLong("216172782113787850"), "userId" : NumberLong(4124) } …………………. |
浮点数一般用52bit的数表示精度，所以52bit的整型应该都没关系。
3.继续检查查询的哪步操作使得它block住了。
不用索引：dropIndex，或者查询时去掉day，用216172782113787850值可以查到。
| > db.user.gift.find({sceneId:216172782113787850}) { "cursor" : "BasicCursor", "nscanned" : 650, "nscannedObjects" : 650, "n" : 0, "millis" : 0, "nYields" : 0, "nChunkSkips" : 0, "isMultiKey" : false, "indexOnly" : false, "indexBounds" : { }, "allPlans" : [ { "cursor" : "BasicCursor", "indexBounds" : { } } ], "oldPlan" : { "cursor" : "BasicCursor", "indexBounds" : { } } } > db.user.gift.find({$query:{sceneId:new NumberLong(216172782113787850)}, $explain:true}) { "cursor" : "BasicCursor", "nscanned" : 650, "nscannedObjects" : 650, "n" : 0, "millis" : 0, "nYields" : 0, "nChunkSkips" : 0, "isMultiKey" : false, "indexOnly" : false, "indexBounds" : { }, "allPlans" : [ { "cursor" : "BasicCursor", "indexBounds" : { } } ], "oldPlan" : { "cursor" : "BasicCursor", "indexBounds" : { } } } > db.user.gift.find({sceneId:216172782113787850}}) Mon Apr 25 13:55:47 SyntaxError: missing ) after argument list (shell):1 > db.user.gift.find({sceneId:216172782113787850}) { "_id" : ObjectId("4dad7840c8b4ebc1064a1f26"), "day" : ISODate("2011-04-18T16:00:00Z"), "earnMoney" : NumberLong(4218), "earnTimes" : NumberLong(35), "fromId" : NumberLong(262), "modifiedTimeLong" : NumberLong("1303214144775"), "receiveMoney" : NumberLong(10505), "receiveTimes" : NumberLong(35), "sceneId" : NumberLong("216172782113787850"), "userId" : NumberLong(4042) …………………. |
看样子在做全表扫描时，mongoDB将每行NumberLong转成了double和sceneId的值进行了比较。
不用orderby：用216172782113787850值可以查到，
| > db.user.gift.find({$query:{day:{$gte:new Date(2011,03,05),$lte:new Date()}, sceneId:216172782113787850}}) |
用916172782113787850查，不存在也不会死
| > db.user.gift.find({$query:{day:{$gte:new Date(2011,03,05),$lte:new Date()},sceneId: 916172782113787850},$orderby:{day:-1}}) |
4.java端
java端使用时不会出现问题，java driver会将long型转换成NumberLong查询
5总结
看样子block是由于orderby+索引+NumberLong用double值引起的。为什么呢？查不到应该也不至于block住，应该是mongoDB用索引查询时的问题。